At present most microbial analysis involves three major steps: primary growth and isolation of an organism from a patient source, biochemical diagnostic tests to make a positive identification, and exposure to antibiotic compounds from which the sensitivities of an organism are determined. Each of the major steps requires a twenty-four hour period to execute. Even though the biochemical identification and antibiotic sensitivities can be run concurrently, the total time required to identify an organism and determine the antibiotic of choice for treatment is usually at least forty-eight hours. Besides the time requirements for setting up the procedures and reading the results, current identification procedures are very labor intensive and often require considerable training and experience on the part of laboratory technicians.
In U.S. Pat. No. 4,576,916 (Lowke et al), a method and apparatus for identifying bacteria using electro-optical investigation is disclosed. In particular, a specified quantity of fluid sample believed to contain a given microbial cell is combined with a portion of a fluid sample with an inhibiting reagent having a known effect on the electrical polarizability of the microbial cell. The resulting fluid sample is then placed in an alternating current electric field to cause the alignment of any microbial cells present. When a polarized beam of laser light is passed through the sample, the extent of birefringence is measured and compared with a reference measurement made with a control.
In U.S. Pat. No. 4,758,509 (Ottley), a method of detection of microbial growth is provided. In this method, a culture of an organism is prepared and a portion is taken for analysis in a pyrolysis mass spectrometer. By monitoring the relative height of the peak in the mass spectrum corresponding to a mass of 60 daltons, an increased height of this peak relative to the remainder of the spectrum indicates growth of the microorganism. A second measurement can also be made corresponding to an abundance of ions at one or more masses. This patent also briefly mentions another method whereby a measurement of optical density is made to detect growth. However, it is indicated that this method is only usable where the culture medium is itself reasonably transparent.
In U.S. Pat. No. 4,384,206 (Bjarno), a process for the detection of particular quality properties in articles of food is disclosed. In particular, this patent discloses a process for detecting "boar taint" in carcasses of non-castrated boars. According to the disclosed method, IR-spectrophotometrical transmission data is determined for the individual carcass or part and this spectral data is compared with corresponding data having a statistical relationship to boar taint.
While various methods have been disclosed in the prior art for determining microbial growth, such methods suffer from a number of drawbacks and are not generally and easily usable.